The overall objective of the proposed research is to investigate the processing strategies used by adults and children in understanding sentences. Reaction-time in picture-sentence matching tasks will serve as the index of comprehension, and specific studies have been designed to delineate (a) the stages in the processing sequence, (b) the nature of the operations performed within stages. All of the studies will use a novel procedure, called the "mismatch" technique, which involves varying the location of the mismatch or difference between a sentence and a picture, and comparing the latencies of subjects' "same-different" responses as a function of whether the mismatch occurred in the sentence subject, verb, or object. The specific issues this technique was designed to clarify include: (1) whether passive sentences are encoded in a surface-structure or deep-structure format; (2)whether the comparison strategy adopted is serial or parallel, exhaustive or self-terminating; (3) whether encoding and comparison strategies are invariant, or change when the order of the stimulus inputs is reversed, or when sentences are changed from an auditory to a visual format; (4) whether sentence voice, negation, and semantic reversibility influence the encoding or the comparison process; (5) whether developmental differences in verification tasks are due to different encoding or comparison strategies; and (6) whether the encoding and comparison strategies adopted by children with, for example, reading difficulties differ from those adopted by "normal" children, and if so how.